The present disclosure relates generally to devices used in identifying two or more points on a horizontal plane, specifically, a fluid-actuated level device for locating points on a level plane.
Numerous level devices have been used to identify points on a horizontal plane. Level devices are particularly useful in the building industries where positioning a structure on a level plane is critical to the design and implementation of the structure. Such structures include, for example, foundations, decks, counter-tops, suspended ceilings, suspended sprinkler systems, pools, fences, and sewer lines. Two level devices are commonly used in the building industries: bubble levels and fluid-actuated levels. Bubble levels are well-known in the prior art. Two types of fluid-actuated levels are generally known in the prior art. Both types operate according to the same general principle: if fluid is allowed to flow through a tube and the end of the tube are raised above the body of the tube, then gravity pulls the fluid such that the fluid-levels at the tube ends settle on the same horizontal plane. The first type of fluid-actuated level generally consists of a sealed tube with a pressure-sensing device connected to a tube end for measuring air pressure in an air cavity at the tube end. The pressure varies with the displacement in air volume at the tube ends caused by the gravitational pull on the fluid; the sensing device may thus be calibrated to a particular air pressure, typically a pressure corresponding to when the fluid-levels in the two ends lie on a horizontal plane. One drawback of the pressure-sensitive fluid-actuated level is its cost, which is often prohibitive for commonplace construction applications.
The second type of fluid-actuated level (generally less costly than the first type) typically uses a fluid-level sensing device connected to an end of an unsealed tube. A fluid-actuated level of this type is disclosed in U.S. Pat. No. 4,434,561 and shown in FIGS. 1-2. In FIG. 1, fluid-actuated level device 10 has a housing unit 17 and a tube 11 for holding an electrically conducting fluid 18, typically tap water. Tube 11 has a reference-end 21, connected to the housing unit 17, and a working-end 20. Working-end 20 is used by a worker for locating level points in a proposed horizontal plane, or reference plane. Housing unit 17 has a base electrode 15 and a reference electrode 14 inserted through the walls of the reference-end 21 for detecting the fluid-level in the tube 11. Electrodes 14, 15 are connected to a power source 12 and a signal generator 13, such as a sound or light generator, and form a circuit when connected. In operation, conducting fluid 18 in reference-end 21 submerges base electrode 15. When a worker lifts the fluid-level in working-end 20 higher, the fluid level in reference-end 21 rises to make contact with reference electrode 14. When conductive fluid 18 contacts reference electrode 14, an electrical circuit is formed which enables current from electrical source 12 to actuate signal generator 13. Signal generator 13 then emits a sound, light or other signal to indicate that the fluid-level in the working-end 20 has contacted the reference plane as defined by the reference electrode 14; this signal will be called the reference signal. In the prior art, housing unit 17 conceals electrodes 14, 15 and reference-end 21; external reference marking 16, which is aligned with the reference electrode 14, is therefore placed on the outside of housing unit 17 to indicate the reference plane to the worker.
FIG. 2 illustrates the general operation of fluid-actuated level device 10. A worker fills tube 11 of fluid-actuated level 10 with fluid and affixes housing unit 17 to, for example, a wall 19. Housing unit 17 is affixed such that external reference marking 16 is aligned with the proposed reference plane 18 (shown as a dotted-line). Working-end 20 (opposite housing unit 17) is shown extended across the wall 19; the water-level in working-end 20 is aligned with reference plane 18. To discover the reference plane, the worker moves working-end 20 upward until the fluid-level in the working-end 20 reaches the same height as the external reference marking 16 on housing unit 17. Due to the action of gravity on the fluid in tube 11 (the body of the tube 11 must be positioned below the tube ends), the fluid within housing unit 17 at this point has submerged base electrode 15 and reference electrode 14; this completes a circuit that activates signal generator 13. The worker hears a reference signal which indicates the level point. In this manner, the working-end 20 may be used to locate a multitude of level points lying on a reference plane roughly defined by a circle centered on housing unit 17 with a radius equal to the tube length. Level points approximately 100 feet from housing unit 17 may be accurately discovered in this manner. The fluid-actuated device of FIGS. 1-2 is especially useful when level points are sought by a worker working alone in rough and un-even terrain, or, for example, where level points need to be discovered around a corner structure. In this case, the worker takes working-end 20 around the corner structure and moves working-end 20 in a vertical manner until a reference signal is heard from housing unit 17.
The fluid-actuated level device of FIGS. 1-2 has a number of limitations. First, the level device 10 does not communicate to the worker whether the fluid-level in the working-end 20 is positioned too high; on the contrary, a single reference signal is given so long as the fluid-level in the working end is either in the reference plane or at any point above the reference plane. This introduces imprecision when a worker, due to, e.g., fatigue or rough terrain, accidentally adjusts the working-end too high after hearing the signal emitted from the device. Second, normal usage of the level device 10 results in dirt and fluid residue accumulation around the electrodes 14, 15 in the tube; this may result in a xe2x80x9cwickingxe2x80x9d effect. Wicking is caused when fluid clings to the dirt and fluid residue around the electrodes to form a conductive bridge between the probes that persists beyond the point at which the fluid-level, under normal conditions, would disconnect the electrodes 14, 15. In the prior art, a worker is unable to efficiently detect a possible wicking condition because visual access to the tube 11 and the electrodes 1415 is not provided. Third, a worker typically affixes the housing unit 17 to a reference plane by aligning a single external reference marking 16 on the outer edge of housing unit 17 to the reference point. Housing unit, however, has a greater width than the tube 11, and therefore any skew or tilt introduced to the housing unit 17 when affixing it (or using it) results in a degree of imprecision equal to the distance between the horizontal planes defined by the reference plane and the external reference marking 16 (the greater the distance, the greater the degree of potential imprecision).
Fourth, housing unit 17 is typically affixed by driving nails or screws for attaching the housing unit 17 into a structure. This often results in imprecision because the nail or screw is driven at an awkward angle due to a lack of care by the worker or by irregularities in the structural medium (e.g., a knot in wood). Because readjustment is typically burdensome (requiring removal and replacement of the nail or screw), such imprecision is typically tolerated. Lastly, the tube ends should generally consist of transparent or otherwise translucent material to enable the worker to view the fluid-levels; as a result, the entire tube is typically constructed of a single molded piece of transparent plastic. Because the tube may be in excess of one-hundred feet long, the cost of transparent tubing may be significant.
A fluid-actuated level device (hereafter, xe2x80x9clevel devicexe2x80x9d) for use, for instance, in the building trades, is disclosed. The level device enables a worker to discover points lying on a horizontal plane defined by a reference point. The level device has a tube with a reference-end and a working-end, and a housing unit attached to the reference-end. Electrodes in the housing unit measure fluid-levels in the reference-end. When the fluid-level in the working-end is positioned in the horizontal plane containing the reference point, then the level device emits a signal; in one embodiment, this signal is a single continuous sound. When the working-end is positioned slightly higher than the reference point, a second signal is emitted; in one embodiment, this signal is an intermittent sound. The second intermittent sound notifies the worker that the fluid-level in the working-end is too high relative to the reference plane, i.e., the worker has xe2x80x9covershotxe2x80x9d the reference plane. Also provided are embodiments having a tube window, an alignment window, and a slidable backing assembly. The tube window provides visual access to the electrodes in the tube. The alignment window enables the reference markers to be in close proximity on adjacent sides of the tube at the reference-end. A slidable backing assembly enables the housing unit to be slidably adjusted along a continuous vertical line after it is affixed to a reference point. Lastly, a method for using a non-transparent tube is provided.